That much was clear at the Fortune Brainstorm Tech conference on Tuesday, when executives from Yahoo, Atlassian, Cornerstone OnDemand, and Lytro gathered to explain why good design is critical to the success of a product and explore what “good design” actually means.

“If the design of software doesn’t allow for simplicity and ease of use,” said Adam Miller, the chief executive of Cornerstone OnDemand, “you don’t get that engagement.”

But simplicity is a complicated subject. We know that people like to use nicely designed things, said Mike Cannon-Brookes, co-chief executive of Atlassian. We know that people want their day to “be as filled with beauty as possible.” We also know that products exist to get a job done. How do you get there?

For Atlassian, “the product has to sell itself.” Despite 1,000 employees, Cannon-Brookes’ company employs just three sales people. To get there, Atlassian puts equal standing between its design, engineering, and product management teams, he said. Then they focus on a customer’s needs. (As opposed to their demands.)

“It’s always customer empathy, right?” he asked the audience. “Design is really about empathy, not beauty. It’s not how it looks, it’s how it works and fits together. At the end of the day, if a customer has a good experience using your product, that’s the end criteria.”

Adam Cahan, senior vice president for mobile and emerging products at Yahoo (YHOO), said that’s why his Sunnyvale, Calif.-based company designs first with mobile devices in mind: to focus.

“In general, design needs and loves constraint,” he said. “If you start with that, you find that you can actually get down to the essence of the product.” And, in theory, the essence of the customer’s problem you’re trying to solve.

Still, there are compromises. Jason Rosenthal, the chief executive of Lytro, acknowledged that his company’s innovative cameras start much more innovative than the result. “You start with this grandiose vision of building the perfect camera,” he said. “Then reality sets in”—in terms of cost, final price, and everything in between.

Still, “it’s quite hard to innovate with zero constraints,” Cannon-Brookes said.

Amazing things can happen when designers and product managers carefully focus on a customer’s use case. Take e-mail, a product with which everyone is familiar, Cahan said. “Why are people pulling refresh all day long?” he asked. The initial reason appears that a person wants more e-mail—but a deeper look reveals that it’s actually boredom at play. “They were bored, and pulling refresh all day long,” he said. “‘Show me something I should care about’ is the mental dialogue.”

“Customer insights are always there,” Cahan added. “You’re usually creating a product based on insight. At the end of the day, nobody typically wakes up and says, ‘Gee, I wish you would redesign this product I use every day.’ ”

But looks don’t hurt.

“You want it to be beautiful and engaging,” Miller said.

“Moments of delight come when it just works for you,” Cahan said.

“We have a lot of design principles, but one of them is gracefully reveal depth,” Cannon-Brookes said. And they all nodded in agreement.